The present invention relates to a process for producing vitamin A which is important in the fields of pharmaceutical preparations, feed or food additives, intermediates thereof, and a process for producing the same.
1. Background Art
As conventional processes for producing vitamin A, there have been known a method of a carbon-increment reaction in a side chain of xcex2-ionone (C13) as a starting material (Pure and Appl. Chem. 66, 1509 (1994)) and a method of coupling C10 sulfones with C10 aldehydes and then eliminating the sulfone group (JP-B 4-3388, JP-B 5-61265 etc.). In the former method, however, xcex2-ionone (C13) as the starting material is very expensive on the market, and in the latter method, a very expensive acetaldehyde derivative is used as an oxidizing agent particularly in an oxidation step in a process for producing the C10 aldehyde, and thus these methods are not always industrially excellent methods.
2. Disclosure of the Invention
Under these circumstances, the present inventors have extensively studied to develop a process for producing vitamin A from inexpensive starting materials, and as a result, they have found that a novel dihalogen derivative can be readily obtained from a triene derivative which can be readily and economically produced from C10 alcohols such as geraniol or linalool. They have also found that vitamin A can be produced via sulfone derivatives from said dihalogen derivatives, thus arriving at the present invention.
That is, the present invention provides:
1. a dihalogen derivative represented by formula (2): 
wherein X represents a halogen atom and R2 represents a protective group for a hydroxyl group,
2. a process for producing a dihalogen derivative represented by formula (2) above, which comprises allowing a halogenating agent to react with a triene derivative represented by formula (4): 
wherein R2 represents a protective group for a hydroxyl group,
3. a process for producing a sulfone derivative represented by formula (1): 
wherein Ar represents an aryl group which may have a substituent group, and R1 represents a hydrogen atom or a protective group for a hydroxyl group, which comprises allowing a sulfone represented by formula (3): 
wherein Ar represents an aryl group which may have a substituent group, to react in the presence of a base with a dihalogen derivative represented by formula (2) above,
4. a sulfone derivative represented by formula (1) above, and
5. a process for producing vitamin A, which comprises allowing a sulfone derivative represented by formula (1) above to react with a base.